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USB hubs - does anything like this exist?
4wd:
as an aside it occurred to me (about 10 minutes after I posted, DUH!) that someone, somewhere must have already done this so I went looking for a DIY version. There are a number of references of multiple port hubs being constructed by gutting a bunch of cheap hubs and mounting them all in a single case (basically daisy chaining), and it doesn't seem like much of a stretch to extend this concept to add a switch and 2 inputs...
3 unpowered and 1 powered (with a suitable power supply) would give me 12 ports...hmmm
-Target (December 29, 2010, 05:01 PM)
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A simple toggle switch to the control lines of a Quad Bilateral Switch, (4066 CMOS or 74HC(T)4066 TTL), is a relatively simple way to do it and it would be self-powered. However, I'd look at making all the ports powered via external means. You're talking about 12 ports, if they are all occupied at a relatively modest power consumption of 100mA, even with 1 powered that's still 1.1A, over twice the specified current sourcing for 1 USB port - which will be where it's coming from.
A more interesting way would be to use a micro-controller, (eg. PIC, Atmel), to monitor the incoming PC USB data lines and through-switch to the devices - more interesting but maybe not more practical since, (as mwb1100 said), Windows would need time to identify all the devices before data could be sent through, so you'd need to incorporate some sort of RAM buffer I'd think or message back to the OS to hold until device ready is signaled.
Target:
A simple toggle switch to the control lines of a Quad Bilateral Switch, (4066 CMOS or 74HC(T)4066 TTL), is a relatively simple way to do it and it would be self-powered. However, I'd look at making all the ports powered via external means. You're talking about 12 ports, if they are all occupied at a relatively modest power consumption of 100mA, even with 1 powered that's still 1.1A, over twice the specified current sourcing for 1 USB port - which will be where it's coming from.
A more interesting way would be to use a micro-controller, (eg. PIC, Atmel), to monitor the incoming PC USB data lines and through-switch to the devices - more interesting but maybe not more practical since, (as mwb1100 said), Windows would need time to identify all the devices before data could be sent through, so you'd need to incorporate some sort of RAM buffer I'd think or message back to the OS to hold until device ready is signaled.-4wd (December 29, 2010, 06:11 PM)
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HA! once a tech, always a tech
my electronics knowledge is rudimentary at best so that's possibly beyond my current abilities (seems like it would need some sort of control circuit to make it work) - I was thinking along the lines of a simple (analog) type switch
4wd:
A simple toggle switch to the control lines of a Quad Bilateral Switch, (4066 CMOS or 74HC(T)4066 TTL), is a relatively simple way to do it and it would be self-powered. However, I'd look at making all the ports powered via external means. You're talking about 12 ports, if they are all occupied at a relatively modest power consumption of 100mA, even with 1 powered that's still 1.1A, over twice the specified current sourcing for 1 USB port - which will be where it's coming from.-4wd (December 29, 2010, 06:11 PM)
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HA! once a tech, always a tech-Target (December 29, 2010, 06:25 PM)
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Thanks! ;D
my electronics knowledge is rudimentary at best so that's possibly beyond my current abilities (seems like it would need some sort of control circuit to make it work) - I was thinking along the lines of a simple (analog) type switch
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Yes, you can try a 2-pole, 2 position switch and just switch the data lines. Power the hub from an external source so you're not switching the power lines as well. Leave the ground connected back to the computers but not the +5V.
You might need some kind of buffering, (not the data type - more to debounce the change-over), but you can certainly try it without first.
DSE - $0.99
Jaycar - $3.95
EDIT: If you want to wait a few hours, (housework - BLAH!), then I can sketch up a simple circuit using the 4066, (or TTL version), and post it up. If you can solder two wires together it shouldn't prove daunting and the components are minimal, say ~$10.
Otherwise I do have another idea that may be mutually beneficial >:D
Target:
Yes, you can try a 2-pole, 2 position switch and just switch the data lines. Power the hub from an external source so you're not switching the power lines as well. Leave the ground connected back to the computers but not the +5V.
You might need some kind of buffering, (not the data type - more to debounce the change-over), but you can certainly try it without first.-4wd (December 29, 2010, 06:49 PM)
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that's more like it :Thmbsup:
so is it acceptable to leave both power lines connected concurrently? I haven't looked at the pinouts yet, but I assume this from your comments
and how would you 'buffer' the change over? I don't anticipate that I would be switching while anything critical was running so I do expect it would be an issue, but now I'm curious
4wd:
Yes, you can try a 2-pole, 2 position switch and just switch the data lines. Power the hub from an external source so you're not switching the power lines as well. Leave the ground connected back to the computers but not the +5V.
You might need some kind of buffering, (not the data type - more to debounce the change-over), but you can certainly try it without first.-4wd (December 29, 2010, 06:49 PM)
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that's more like it :Thmbsup:
so is it acceptable to leave both power lines connected concurrently? I haven't looked at the pinouts yet, but I assume this from your comments-Target (December 29, 2010, 07:07 PM)
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I wouldn't call it acceptable, there's a risk of destroying the USB device or you may have the two computers fighting each other if the voltage supply isn't exactly the same.
Since you'd be having one powered port anyway, (for external 2.5"), you might as well power them all externally - plus it's so easy :)
EDIT: Just to expand on the underlined bit. If you switch the +5V then you're effectively disconnecting the power and reconnecting within a very short space of time. This could induce a voltage spike into the device but I look at it this way: I wouldn't do it to my whole system, a television, or any electronic device since it has been proven in the past to kill devices.
If you leave both connected then a fault in one computer could possibly feedback into the other - why take the chance?
I prefer to leave the USB devices powered and just switch the data lines, there's less chance of a voltage spike being induced into the data lines that way also.
and how would you 'buffer' the change over? I don't anticipate that I would be switching while anything critical was running so I do expect it would be an issue, but now I'm curious
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Did you mean don't ?
Possibly just a couple of CMOS/TTL chips wired to input/output lines, the problem being looking through specs to find what's capable of >480MHz switching. I'd need to look through my circuit library and check the web to get a better idea and see how critical it'd be.
See my edit to my previous post also.
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